Study on Corrosion and Wear Behavior Mechanism of Reactor Material in Metastannic Acid Synthesis

Abstract

AISI 316L, Ti2, and Zr1 are widely used in the selection of reaction still material, however, there is corrosion wear behavior in the use process. In this paper, the adsorption behavior of oxygen in Fe, Ti, and Zr is studied by the first principles method. Corrosion and wear behaviors of AISI 316L, Ti2 and Zr1 were studied by electrochemical corrosion and wear tests. The results show that AISI 316L can effectively resist the action of friction pair during wear by elastic modulus calculation. Oxygen is easily adsorbed at the top of the Fe(111) crystal plane and the bridge site of the Zr(110) crystal plane to form the most stable adsorption structure. The Ecorr of Zr1 (0.275 V) is greater than that of Ti2 (0.266 V) and AISI 316L (0.094 V), resulting in a ZrO₂ passivated film with strong protection in the HNO3 solution. The wear rate of AISI 316L is higher than that of Zr1 and Ti2. In the selection of tin chemical reactor material, it is preferred that Zr1 can withstand corrosion and wear for a long time in a nitric acid system, which provides important guidance for corrosion and wear of reactor materials in the synthesis of tin acid.

1. Introduction

AISI 316L, Ti2, and Zr1 are widely used in the selection of reaction still material, however, there is corrosion wear behavior in the use process. Researching the corrosion and wear mechanism of materials and improving the wear and corrosion resistance of materials is the difficulty and focus of materials research at this stage [1,2,3].

At present, corrosive wear behavior has attracted the interest of researchers, and a number of studies have been conducted on corrosive wear behavior [4,5,6]. Bateni et al. [7] studied the frictional behavior of AISI 304 stainless steel under simultaneous wear and corrosion using 3.5 wt.% NaCl solution as a corrosive agent. Li et al. [8] investigated the erosion-corrosion behavior of Ti and Zr under acidic conditions, the addition of oxide layers on the Ti and Zr surfaces improved the corrosion resistance of the materials. The above studies found that stainless steel, Ti, and Zr have good corrosion wear resistance. During the synthesis of metastannic acid in the tin chemical industry, both the erosion-corrosion caused by strong acids and the abrasion of tin particles create a complex corrosive wear environment for the reactor [9]. The AISI 316L stainless steel, Ti, and Zr are the main choices for the manufacture of reactors. There are few studies on the corrosion wear of reactor materials under strong acid conditions.

In order to further clarify the problem of corrosion and wear mechanisms of reactor materials in metastannic acid synthesis: Firstly, this paper analyzes the corrosivity of Fe, Ti, and Zr from the microscopic atomic point of view based on the first-principles. Secondly, electrochemical corrosion and wear tests are used to study the corrosion and wear behavior of AISI 316L, Ti2, and Zr1 from a macroscopic point of view. The results will provide an important guide to the corrosive wear of reactor materials in the synthesis of metastannic acid.

2. Calculations and Experimental Methods

2.1. First-Principles Calculations

The Fe crystal cell is a body-centered cubic structure (bcc), the cell group is IM-3M, the lattice constant a₀ = b₀ = c₀ = 2.8664 Å, α = β =, and γ = 90°. The Ti crystal cell is a dense stacked hexagonal structure (hcp), cell group is P63/MMC, lattice constant a₀ = b₀ = 2.9506 Å, c₀ = 4.6788 Å, α = β = 90°, and γ = 120°. The Zr crystal cell is a dense stacked hexagonal structure (hcp), the cell group is P63/MMC, the lattice constants a₀ = b₀ = 3.2312 Å, c₀ = 5.1477 Å, α = β = 90°, γ = 120°. The accuracy of the calculation for the original cell expansion cell for the 2 × 2 × 2 supercell is shown in Figure 1.

All calculations in this study are based on the first-principles approach of density functional theory (DFT), using the generalized gradient approximation of the PBE (Perdew–Burke–Ernzerhof) method [10]. Generalized gradient approximations using GGA functions are used to describe electron exchange and correlation [11,12]. The solution of the generalized Kohn–Sham equation is performed by an efficient iterative matrix diagonalization routine [13]. Based on the convergence test, the cut-off energy plane wave for bulk phase calculation was set to 420 eV; the cut-off energy plane wave for oxygen adsorption model calculation was set to 600 eV. Meanwhile, the valence electrons considered for Fe, Ti, and Zr are 3d⁶4s², 3d²4s², and 4d²5s², respectively. Assuming all atoms are neutral, the K points for the bulk phase calculation were set to (4 × 4 × 4), and the K points for the adsorption model (5 × 5 × 2). The self-consistent field (SCF) convergence value was set to 1 × 10⁻⁵ eV/atom and the whole structure was relaxed to obtain the ground state by using the Broyden–Fletcher–Goldfarb–Shannon (BFGS) algorithm, in which the unitary parameters and fractional coordinates of the atoms were optimized simultaneously [12]. To avoid non-physical interactions due to long-range electrostatic effects, a vacuum layer of 10 Å is added to the adsorption structure. Considering the computational accuracy and time cost, the convergence value of the total energy per atom is set to 1 × 10⁻⁵ eV/atom, the stress on a single atom is less than 0.4 eV/nm, the stress deviation is less than 0.1 GPa, and the tolerance offset is less than 0.01 nm.

2.2. Materials and Methods

This study used AISI 316L stainless steel (GB/T 20878-2007), Ti2 (GB/T3620.1-2016), and Zr1 (GB/T21183-2007) as samples. The samples were analyzed in physical phase using a Rigaku-Ultima X-ray diffractometer (Rigaku, Tokyo, Japan), the experiments were performed at 40 kV and 30 mA of Cu-Ka radiation. The scanning step size was 0.02, the time interval was 1 sec/step, and the scanning range was 20–100°. The XRD test results for samples AISI 316L, Ti2, and Zr1 are shown in Figure 2. The AISI 316L stainless steel has Fe_10.8Ni and γ-Fe as the main phases, Ti2 phase shows pure Ti phase, and Zr1 phase shows pure Zr phase.

Electrochemical corrosion open circuit potentials, Tafel curves, and impedance spectra of AISI 316L stainless steel, Ti2, and Zr1 were tested in 20 wt.% HNO3 solution using a CS310X multi-channel electrochemical workstation. All experiments were performed at 25 °C in a 100 mL reactor filled with a corrosive medium solution using a three-electrode system with a saturated glycury electrode (SCE) as the reference electrode, all potentials being relative to the SCE, and a platinum electrode as the auxiliary electrode. Each sample is attached to a copper wire and mounted in epoxy resin in such a way that 1 cm² of the surface area of the sample can be exposed to the test solution. The self-corrosion potential Ecorr and corrosion current density Icorr were obtained by the polarization curve using the epitaxial method. Microhardness study with VH-5 digital microhardness tester with Vickers indenter and average hardness values were obtained from 5 identical measurements. The friction and wear tests on AISI 316L, Ti2, and Zr1 were conducted at room temperature using a Rtec reciprocating friction and wear tester (Rtec, MFT-5000, Rtec instruments, San Jose, CA, USA). The medium for the dry friction experiment is air, and the counterpart is a WC ball with a diameter of 6 mm, and the same experiment needs to be repeated three times to improve the reliability of the data. Wear profile scanning used a Rtec-3D profilometer (Rtec, UP-Dule Mode, Rtec, San Jose, CA, USA). Scanning electron microscopy was used to observe the electrochemical corrosion and wear morphology, and the composition of the corroded surfaces of the samples was analyzed using an energy spectrometer (EDS) equipped with SEM (Zeiss SEM EVO18, Oberkochen, Germany).

3. Results and Discussion

3.1. Computational Analysis

The optimized geometric structures of Fe, Ti, and Zr are shown in Figure 1, the optimized lattice constants are: a₀ = 2.8664 Å, a₀ = 2.9506 Å, and a₀ = 3.2312 Å, respectively, which are in good agreement with the experimental results [14,15,16], indicating that the calculated parameters are set within a reasonable range. After obtaining a stable cell configuration, it is convenient to calculate the elastic constants, surface energy, and electronic structure of the bulk phase, followed by subsequent surface adsorption calculations.

3.1.1. Mechanical Properties Analysis

The elastic constant is the quantity used to characterize the elasticity of a material and is a fourth-order tensor, calculated from Hooke’s law. Since the calculated crystal is a cubic crystal system, there are three independent elastic constants: C₁₁, C₁₂, and C₄₄. According to Born–Huang’s lattice dynamics theory [17,18], the criterion of mechanical stability of a cubic crystal system is [19]:

$$C_{11}>\left|C_{12}\right|,C_{44}>0,\left(C_{11}+2C_{12}\right)>0$$

(1)

The calculated elastic constants satisfy the above conditions, indicating that the Fe, Ti, and Zr phases are mechanically stable structures. The modulus of elasticity of a cubic crystal system is calculated as follows [20,21,22,23,24]:

$$B_V=\frac{1}{9}[2\left(C_{11}+C_{12}\right)+C_{33}+C_{44}]$$

(2)

$$B_R=\frac{1}{3}\left(C_{11}+2C_{12}\right)$$

(3)

$$G_V=\frac{1}{5}\left(C_{11}-C_{12}+3C_{44}\right)$$

(4)

$$G_R=\frac{5(C_{11}-C_{12})C_{44}}{\left[4C_{44}+3\left(C_{11}-C_{12}\right)\right]}$$

(5)

$$B_H=\frac{B_V+B_R}{2}$$

(6)

$$G_H=\frac{G_V+G_R}{2}$$

(7)

where B_V, G_V, B_R, G_R, B_H, and G_H were estimated by the Voigt–Reuss–Hill method approximation of the bulk modulus and shear modulus, respectively [25]. The bulk modulus (B) and shear modulus (G) of Fe, Ti, and Zr were calculated by the Voigt–Reuss–Hill approximation of CASTEP, as shown in

Table 1. Elastic constants for polycrystalline material (GPa).

Bulk	C11	C12	C44	BV	GV	BR	GR	BH	GH
Fe	192.52	109.37	47.37	137.18	45.12	137.17	44.95	137.17	45.03
Ti	181.75	71.23	42.61	110.26	50.74	110.14	49.75	110.20	50.24
Zr	175.06	55.12	24.958	99.74	45.05	99.71	37.71	99.73	41.38

. The bulk modulus reflects the resistance of the material to external homogeneous compression in the elastic regime, and in addition, a large shear modulus indicates a strong rigidity of the material. The maximum bulk modulus of Fe is 137.17 GPa, and the maximum shear modulus of Ti is 50.24 GPa. It can be predicted as a reactor material can well resist the impact and shear effect of the load, and in the process of wear, AISI316 stainless steel can well resist the effect of friction.

Young’s modulus can express the stiffness of the material, and Young’s modulus (E) is calculated as in Equation (8) [26]:

$$E=\frac{9B_H{G}_H}{3B_H+G_H}$$

(8)

Poisson’s ratio (σ) is the absolute value of the ratio between the transverse and longitudinal strains of the material, and the formula for calculating Poisson’s ratio is Equation (9) [27]:

$$\sigma =\frac{3B_H-2G_H}{2\left(3B_H+G_H\right)}$$

(9)

Young’s modulus and Poisson’s ratio are calculated as shown in

Table 2. Calculated values of Young’s modulus €, Poisson’s ratio (σ), hardness, and general anisotropy index (A^U) for Fe, Ti, and Zr (GPa).

Bulk	E	σ	HV	AU
Fe	121.77	0.305	3.84	0.019
Ti	130.85	0.302	4.03	0.10
Zr	109.04	0.320	4.72	0.97

. The Young’s moduli of Fe, Ti, and Zr were 121.77, 130.85, and 109.04 GPa, respectively, and the Poisson’s ratios were 0.305, 0.302, and 0.320, respectively. The larger Young’s modulus, the less prone to deformation. Ti is not easily deformed under the action of external forces and has the best stiffness. The harder the material, the smaller the Poisson’s ratio; the softer the material, the higher the Poisson’s ratio. The smallest Poisson’s ratio was for Fe, which can have good stiffness when subjected to load.

The anisotropy index reflects an important index of the plastic behavior of the material, i.e., the universal anisotropy index (A^U) can be calculated by the following equation [28]:

$$A^U=5\frac{G_V}{G_R}+\frac{B_V}{B_R}-6$$

(10)

The larger the A^U value, the stronger the anisotropy of the compound. As can be seen from Table 2, the calculated A^U values of Fe, Ti, and Zr are greater than zero, and Zr has the strongest anisotropy. According to the semi-empirical hardness formula proposed by Tian [29], it is defined as Equation (11):

$$H_V=0.92K^{1.137}{G}^{0.708},K=G_H/B_H$$

(11)

The predicted hardness of Fe, Ti, and Zr (Table 2), the lower the B/G, the higher the H_V. Zr has the largest H_V, which is consistent with the experimental results. The comprehensive analysis predicts that in wear, AISI 316L is effective against frictional subsets, followed by Zr and Ti.

3.1.2. Oxygen Adsorption Analysis

In order to calculate the surface reaction of Fe, Ti, and Zr in a dilute nitric acid corrosive environment, due to the strong acidic and oxidizing properties of nitric acid, Fe, Ti, and Zr are usually oxidized during the corrosion process to produce a passivation film to hinder the corrosion process. Hence, we adsorbed oxygen atoms on the surfaces of Fe, Ti, and Zr and calculated the adsorption behavior of oxygen on Fe, Ti, and Zr. In general, adsorption tends to be on crystalline surfaces with high surface energy. The higher the surface energy of the crystalline surface, the more active the electron movement on the surface, which facilitates the adsorption. The surface energy is calculated for the low index crystal surfaces of Fe, Ti, and Zr, and the surface energy calculation formula is shown in Equation (12) [30,31]:

$$\sigma =\frac{E_{slab}-\left(\frac{n_{slab}}{n_{bulk}}\right)E_{bulk}}{2A_{surf}}$$

(12)

where E_slab is the total energy of the fully relaxed surface, E_bulk is the optimized energy of the cell body phase, A is the surface area, and n is the total number of atoms of Vit1 or Zr in the surface crystal cell.

The surface energy calculations for the low-index surfaces of Fe, Ti, and Zr are shown in Figure 3. From Figure 3, it can be seen that the surface energy of Fe is ranked as (111) > (210) > (100) > (211) > (110), so the surface energy of (111) surface of Fe is 3.318 J/m², which is the most active to the corrosive environment. The surface energy of Ti is (111) > (110) > (100) > (001), so the surface energy of (111) surface of Ti is 2.6414 J/m², which is the most active in the corrosive environment. The surface energy of Zr is (110) > (010) > (100) > (111) > (001), so the surface energy of (110) surface of Zr is 1.8666 J/m², which is the most active to the corrosive environment. In the adsorption interfacial binding, there are three coordination relationships: top site, bridge site, and hollow site, considering the different ways of atomic binding at the interface. Therefore, we are focused on the adsorption behavior of oxygen adsorption on the top, bridge, and hollow sites of Fe(111), Ti(111), and Zr(110) surfaces, and the established model is shown in Figure 4.

The adsorption energy is an indicator for the adsorption phenomenon to measure the ease of the adsorption, and the adsorption energy is calculated for the above nine models to discuss O adsorption from the perspective of adsorption energy. For the convenience of discussion, the oxygen atom adsorption energy is defined by the following Equation (13) [32].

$$E_{ad}=\frac{E_{gra}+N{E}_O-E_{tot}}{N}$$

(13)

where E_tot is the total energy of the system after atom adsorption, E_gra is the total energy of the corresponding system before adsorption, E_O is the total energy of isolated O atoms, and N is the number of adsorbed atoms. The higher the adsorption energy, the more stable the structure obtained indicating that the adsorption process is more easily occurring. As shown in Figure 5, the adsorption energy of the top site of the oxygen-adsorbed Fe(111) crystalline surface is greater than that of the bridge site and hollow site, which indicates that the top site of oxygen-adsorbed Fe(111) crystalline surface is more stable. The adsorption energy of the hollow site of the oxygen-adsorbed Ti(111) crystal surface is greater than that of the top site and bridge site, and the hollow site of the oxygen-adsorbed Ti(111) crystal surface is more stable. The oxygen-adsorbed Zr(110) crystal plane has the largest adsorption energy at the bridge site and the most stable adsorption structure.

The work function is the thermodynamic work required to move the electrons out of the material to a resting state in the vacuum near the surface. The work function W for a given surface is defined by Equation (14) [33]:

$$W=-e_{\phi }-E_f$$

(14)

where −e is the charge of the electron, φ is the electrostatic potential in the vacuum near the surface, E_f is the Fermi energy level (electrochemical potential of the electron) inside the material, and −e_φ is the energy of the electron at rest in the vacuum near the surface. As shown in Figure 6b, oxygen adsorption of Fe(111) crystalline surface top sites after the electron escape becomes difficult, forming a stable adsorption structure. The oxygen adsorption Ti(111) crystal surface work function is not very different, and the oxygen adsorption Zr(110) crystal surface has the largest bridge site work function and the most stable adsorption structure.

3.2. Electrochemical Corrosion Analysis

The use of electrochemical testing methods can effectively simulate the study of the corrosion performance of materials under actual working conditions. Measurements of open circuit potentials, polarization curves, and impedance spectra were used to evaluate the corrosion resistance of AISI 316L, Ti2, and Zr1 alloys in environments containing 20 wt.% HNO₃ solutions. Generally, AISI 316L, Ti2, and Zr1 alloys are subject to severe surface corrosion in environments containing 20 wt.% HNO₃ solutions due to the presence of corrosive anodic reactions and the following cathodic reactions [34,35,36,37]:

Anodic reactions:

$$\mathrm{Fe}\to {\mathrm{Fe}}^{2+}+2{\mathrm{e}}^{-}$$

(15)

$$\mathrm{Ti}\to {\mathrm{Ti}}^{4+}+4{\mathrm{e}}^{-}$$

(16)

$$\mathrm{Zr}\to {\mathrm{Zr}}^{2+}+4{\mathrm{e}}^{-}$$

(17)

Cathodic reactions:

$$2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2$$

(18)

$${\mathrm{O}}_2+4{\mathrm{H}}^{+}+4{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2\mathrm{O}$$

(19)

The value of the open circuit potential can characterize the corrosion potential of the material, the higher the open circuit potential the more corrosion-resistant the material [38]. Figure 6a shows the stable open circuit potential of the sample corroded in the environment of 20 wt.% HNO₃ solution for 800 s. The potential values of Zr1 are higher than Ti2 and AISI 316L under the same conditions, indicating that Zr1 is more corrosion resistant than Ti2 and AISI 316L in the nitric acid system, which is related to the fact that HNO₃ is a strong oxidizing acid. The samples were subjected to Tafel polarization curve measurements, and the self-corrosion potential and corrosion current density of the material were solved by Tafel extrapolation to evaluate the corrosion resistance of the material [39]. Figure 6b shows the Tafel curves for AISI 316L, Ti2, and Zr1 with the tip of the curve corresponding to the open circuit potential of the material. The self-corrosion potential and corrosion current density obtained by solving for the Tafel curve are shown in

Table 3. Analysis of Electrochemical Parameters of Corrosive Environment Samples by Tafel Extrapolation.

Specimen	Icorr (A·cm−2)	Ecorr (V)
AISI 316L	1.9113 × 10−5	0.094
Ti2	1.0928 × 10−5	0.266
Zr1	2.2660 × 10−6	0.275

. The corrosion current density of Zr1 is lower than that of Ti2 and AISI 316L. The corrosion current density of AISI 316L in 20 wt.% HNO₃ solution is the largest and the self-corrosion potential is the lowest, indicating that AISI 316L has poor corrosion performance in the HNO₃ system. Although AISI 316L has excellent corrosion resistance and can be safely used in environments containing halogen ions such as Cl⁻ [40], AISI 316L cannot be less than oxidizing for strong oxidizing acids such as HNO₃, rendering the surface passivation film useless.

Figure 7a shows the Nyquist plots of AISI 316L, Ti2, and Zr1 in 20 wt.% HNO₃ solution. The results show that Zr1 has the largest capacitive arc radius and the highest corrosion resistance. Figure 7b shows that the low-frequency region corresponds to the sum of Rs and Rp, indicating the corrosion resistance of the material, with Zr1 having the highest resistance value and the most corrosion resistance. Figure 7c represents the capacitive resistance of the equivalent circuit. The curves are all positive peaks and no negative peaks and valleys, indicating the absence of inductive phenomena. The equivalent circuit diagram of Figure 7d was chosen for impedance fitting, and the impedance fitting data are listed in

Table 4. Parameters of the AC impedance spectrum of the material measured in 20 wt.% HNO₃ solution.

Specimen	Rs (Ω·cm2)	Rp (Ω·cm2)	CPE-T (F·cm−2)	CPE-P
316L	2.023	735.71	1.2467 × 10−4	0.83804
Ti2	2.110	7904.6	6.9888 × 10−5	0.88789
Zr1	71.152	9451.8	1.598 × 10−5	0.84711

, where Rs is the solution resistance, Rp is the polarization resistance, CPE-T is the bilayer capacitance, and CPE-P is the dispersion index [41]. The polarization resistance of Zr1 was significantly higher than that of Ti2 and AISI 316L, indicating that a dense passivation film was formed on the surface of Zr1, which prevented the oxidation of nitric acid and protected the substrate from corrosion. Although AISI 316L can also form Cr oxides, and eventually forms a Cr-rich inner layer and Fe-rich outer layer of the double film structure, in front of the strong oxidizing nitric acid it seems to lose the protective effect. The dispersion indices of AISI 316L, Ti2, and Zr1 are essentially the same, close to 1, indicating that the metal-solution interface double layers of all three samples are close to the ideal capacitive behavior.

Further explanations of the corrosion mechanisms of materials were gained using scanning electron microscopy and energy spectroscopy. The SEM and EDS spot sweep of AISI 316L stainless steel, after corrosion, is shown in Figure 8. The surface sweep of corrosion shows the possible presence of various passivation films on the surface, such as CrO₃, Cr₂O₃, FeO, and NiO. Further scanning of the corrosion pits found that the surface was mainly Fe, Cr, Ni, and O, with a small amount of Mo, Si, and Mo elements. However, it was clearly found that AISI 316L in 20 wt.% HNO₃ solution produced a large number of corrosion pits and localized areas of serious exfoliation; AISI 316L corrosion can clearly be seen on the grain boundaries of the material and exfoliation pits are along the grain boundaries. This indicates that nitric acid has caused severe damage and the surface passivation film has lost its protective effect. Figure 9 shows that some white pitting pits are produced after Ti2 corrosion, the surface is not corroded out of grain boundaries, and the surface is relatively smooth. EDS analysis showed that the surface elements were mainly Ti, and there were O elements around the corrosion pits. It is speculated that the passivation film is TiO₂. Figure 10 shows that there are no obvious extensive pitting pits found after the corrosion of Zr1, and the surface is relatively smooth. The EDS analysis showed that there were trace Hf elements and a large number of Zr and O elements on the surface, and the passivation film on the surface was ZrO₂.

The corrosion analysis shows that Zr1 is the best material among the three materials in terms of corrosion resistance and can be used as the choice of reactor material for the synthesis of dilute acids, which has particularly excellent corrosion resistance.

3.3. Micro-Hardness and Friction Wear Analysis

The results of the micro-Vickers hardness test on the samples are shown in Figure 11. The hardness of Zr1 is 179.9 HV, which is greater than that of AISI 316L and Ti2, among which Ti2 has the lowest hardness value indicating that Zr has good mechanical properties. Analysis of the wear of AISI 316L, Ti2, and Zr1 after 1 h of wear under dry friction conditions of 100 N: At present, there is no unified standard for the assessment of wear and tear. The common evaluation methods are wear quantity, wear rate, and wear resistance, and the wear rate is generally used to measure wear in corrosion wear; therefore, the wear rate is used to characterize the wear as the amount of wear per unit friction distance. The wear volume ΔW of the alloy sample is measured by the contour method, and the wear rate W_S of the alloy is calculated according to Equation (20) [42]:

$$W_s=\frac{\Delta W}{S\times N}$$

(20)

where N is the normal load and S is the frictional distance.

The friction coefficients after wear are shown in Figure 12a. The average friction coefficient of AISI 316L is about 0.5. The average coefficient of friction of Ti2 and Zr1 is close to about 0.36, with the smallest fluctuation. The reason for the minimal fluctuation may be the formation of a lubricating film between the contact sliding surfaces [43]. For Ti2 and Zr1, as the friction proceeds friction pair in the early stages of wear, due to the surface roughness value of the pair surface being larger, the actual contact area is smaller, and the number of contact points and the area of most contact points is larger, so the contact point adhesion is serious, the wear rate is larger, and the friction coefficient rises sharply. However, as the wear proceeds, the surface micropeak peaks gradually wear away, the surface roughness value decreases, the actual contact area increases, the number of contact points increases, the wear rate decreases, and the friction coefficient decreases creating the conditions for the stable wear stage. As the wear progresses, the wear enters the stable wear stage, where the wear is slow and stable, the wear rate remains basically unchanged, and the friction coefficient area is smooth in the normal wear stage. However, with AISI 316L stainless steel in the early stage of wear, due to the surface oxidation layer of the friction coefficient, it rises and then falls in friction to a stable phase. The friction coefficient decreases sharply at 500 s, indicating that the wear removes surface abrasives and produces an oxide layer that reduces the surface roughness. Then, it enters the stable wear phase. The phenomenon of a sharp drop in the coefficient of friction occurs again at 1500 s, which is caused by the continuous generation of an oxide layer on the material and then peeling off. In the late stage of wear, the friction coefficient increases, the wear surface becomes rough, and the wear is more serious [44]. The results of the wear rate calculation are shown in Figure 12b, although the hardness of Zr1 is the largest, the wear rate of AISI 316L stainless steel is the smallest after 1 h of wear under the action of 100 N, which can resist the action brought by the frictional substrate, and the wear rate of Ti2 is the largest and is in the lose efficacy state. Due to the high hardness and multiple-phase compositions of AISI 316L, the material has good stiffness and resistance to wear loads. The three-dimensional morphology and cross-sectional depth of AISI 316L, Ti2, and Zr1 after wear can be seen in Figure 13, which shows that the wear pits of AISI 316L are smaller than those of Ti2 and Zr1. The wear width of AISI 316L is about 1.52 mm which is 53% less than that of Ti2 (3.22 mm), showing excellent wear resistance. The depth of the cross-section shows that AISI 316L has the shallowest depth and Ti2 has the greatest depth of wear marks. The cross-sections of AISI 316L and Ti2 are relatively gentle and the cross-section of Zr1 has a large wear undulation. Therefore, for dry friction conditions, AISI 316L has the best wear resistance, followed by Zr1 and finally Ti2.

Further analysis of the wear mechanism of materials using SEM is critical, Figure 14 and Figure 15 show microscopic observations from the surface of the abrasion marks and the dissected cross-section, respectively. The bottom of AISI 316L stainless steel wears with a clear delamination phenomenon, producing a smooth and flat surface with severe plastic deformation and plow marks clearly parallel to the direction of friction. Due to the role of friction, AISI 316L stainless steel is subjected to repeated external forces that make the surface organization of the process hardening phenomenon, the surface of the oxide layer, so that wear cannot continue down the role. From Figure 14a–c, the AISI 316L stainless steel wear cross-sectional morphology shows the microscopic presence of wear spalling pits, there is severe plastic deformation, cracks in the spalling pits to expand, and did not continue to expand deep into the matrix. The wear surface of AISI 316L stainless steel has cracks and signs of debris shedding, and the material shedding has a lamellar character (Figure 14c). Its wear mechanism should be a mixed mechanism of abrasive wear and adhesive wear and the main abrasive wear is the same. It is observed from Figure 14d–f that Ti2 wears more severely, producing extensive breakout pits accompanied by obvious delamination spalling. A large number of cracks are produced at the bottom of the spalling pits generated by wear showing signs of expansion deeper into the substrate. The wear surface shows a furrow shape and a large number of abrasive chips adhering to the surface. A large number of breakout pits are found in the Ti2 wear from Figure 15e,f. There are a large number of cracks inside the wear pit, and the surface and matrix are caused by the delamination phenomenon extending deep toward the matrix, which is the reason for the poor wear resistance of Ti2. The wear of Zr1 observed in Figure 15g–i shows a plow furrow morphology with delamination of the surface layer. The surface of Ti2 is relatively flat and no cracks are found to expand into the matrix. There are also some cracks inside the spalling pits.

Combined with the friction coefficient change and hardness comprehensive analysis, in the wear process, AISI 316L, Zr1, and Ti2 surface layers produce a thin oxide layer that can resist the role of the friction sub for a short time. As the friction proceeds, the oxide layer grows to a certain thickness, and under the repeated action of friction, the oxide layer produces microscopic cracks, resulting in the oxide layer falling off and the material wearing more seriously. Analysis by the theory of adhesive wear [45], the metal surface plastic deformation, is that the contact area of the friction pair becomes larger, the relative sliding of the oxide film ruptures, the formation of a new contact at the contact continues to slide the contact shear, followed by the formation of a new contact, repeatedly on the material wear effect. The wear process generates a large number of abrasive chips acting as abrasive grains, which are pressed into the local area of the substrate by the friction substrate to a deformation fracture [46]. The vertical pressure of the friction sub makes the abrasive chips embed in the surface, and the horizontal force of reciprocal sliding makes the chips perform chip movement on the surface, causing tangential deformation and fracture of the surface. Because of the long wear time, alternating stresses are generated on the wear surface due to the cyclic loading action, resulting in severe plastic deformation. The surface develops cracks, which gradually expand and fracture, causing the material to spall and a large number of spalling pits to appear. Therefore, the wear mechanism of AISI 316L, Zr1, and Ti2 is the interaction of adhesive wear, abrasive wear, and surface fatigue wear.

In the tin chemical reactor, Zr1 material selection is preferred, which can be used in the nitric acid system for a long time, the surface of the ZrO₂ passivation film can be well below the nitric acid erosion effect, and in the tin chemical reaction, there is wear and tear brought by tin particles. The wear-resistant surface of Zr1 is also excellent, and the high hardness of the substrate is used to reduce the generation of wear under external forces.

4. Conclusions

This paper explains the effects of oxygen on the corrosion performance of Fe, Ti, and Zr through first principles, followed by electrochemical corrosion and wear tests to study the corrosion and wear behavior of 316L stainless steel, Ti2, and Zr1, leading to the following conclusions:

(1) The modulus of elasticity calculation predicts that, in wear, AISI 316L can effectively resist the action of frictional substrates, followed by Zr and Ti. Oxygen is easily adsorbed at the top site on the Fe(111) crystal plane, the hollow site on the Ti(111) crystal plane, and the bridge site on the Zr(110) crystal plane to form a stable adsorption structure.

(2) The corrosion performance of Zr1 is better than Ti2 and AISI 316L, producing a ZrO₂ passivation film with strong protection in HNO₃ solution.

(3) The best wear resistance is AISI 316L, followed by Zr1 and finally Ti2, and the wear mechanism is the interaction of adhesive wear, abrasive wear, and surface fatigue wear. The preferred choice of material for a tin chemical reactor is Zr1 which can withstand corrosion and wear in the nitric acid system for a long time.